We have analyzed the coupling of ultraintense lasers (at 2 1019 W=cm2) with solid foils of limited transverse extent (10 s of m) by monitoring the electrons and ions emitted from the target.We observe that reducing the target surface area allows electrons at the target surface to be reflected from the target edges during or shortly after the laser pulse. This transverse refluxing can maintain a hotter, denser and more homogeneous electron sheath around the target for a longer time. Consequently, when transverse refluxing takes places within the acceleration time of associated ions, we observe increased maximum proton energies (up to threefold), increased laser-to-ion conversion efficiency (up to a factor 30), and reduced divergence which bodes well for a number of applications.
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机译：我们通过监测靶材发出的电子和离子，分析了超强激光（2 1019 W = cm2）与有限横向范围（10 s of m）的固体箔片的耦合。观察到减小靶材的表面积可以使电子在激光脉冲期间或之后不久从目标边缘反射的目标表面上的光。这种横向回流可以在目标周围保持更热，更密实和更均匀的电子鞘层更长的时间。因此，当在相关离子的加速时间内发生横向回流时，我们观察到最大质子能量增加（最多三倍），激光到离子的转换效率增加（最多30倍），并且发散减小，这对于大量的应用程序。
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